Disk drive systems have been used to store information for computers for many years. With the advent of laptop computers and the progressive reduction in size of portable computers, there is an increasing demand for reducing the size of disk drive systems while at the same time increasing the memory capacity thereof.
The disk storage systems of the prior art are typically in the form of a rectangular housing which has predetermined size dimensions. For instance, the standard package height for a 31/2 Winchester disk drive system has been set by the industry at approximately 1". This package height of the disk drive system is known in the disk drive art as the "Z-height".
Further reductions in the size of disk drive systems have been fostered by the introduction of laptop computers. As, for example, is discussed in U.S. Pat. No. 4,933,785, a hard disk utilized in a disk storage system employed in laptop computers has a diameter of approximately 2.5 inches. However, the overall Z-height of the disk drive system of U.S. Pat. No. 4,933,785 remained unchanged at approximately 1".
While utilizing approximately 2.5" diameter hard disks, U.S. Pat. No. 5,025,336 discloses a disk drive system having an overall Z-height which is less than 1". In order to attain this result, the disk drive system of this patent reduces the height dimension of the spin motor (i.e. the motor which rotates the disks) by reducing the height of the permanent magnet which produce a magnetic field which causes the rotor assembly of the spin motor to rotate. The height of the permanent magnets utilized in U.S. Pat. No. 5,025,336 is reduced by employing magnets made of a material that includes a rare earth, such as neodymium or samarium. Utilization of these materials, however, is disadvantageous as they add significant overall expense and are not readily available for mass production. Further, as is discussed below, this disk drive system still employs conventional mechanical fasteners to secure the spin motor to the lower plate.
In order to reduce the Z-height of a disk drive system, prior designs have primarily focused, in part, on the means for securing the top cover to the lower base plate of the housing as well as the means for joining the spin motor to the lower base plate. For instance, in one data storage system (i.e., the data storage system in U.S. Pat. No. 5,021,905), the top cover enclosing the disk drive environment is screwed to the lower base plate of the disk drive housing. It has been found, however, that screwing the top cover to the lower base plate of the disk drive housing results in warping and distortion of the head disk assembly due to the imperfect mating of parts. Due to this imperfect mating of parts, positional offset errors of the magnetic heads can often result.
Further, mechanical fasteners, screws, clips, etc. which have been traditionally used to fasten the top cover to the lower base plate have been difficult for fully automated assembly operations to properly handle. It has therefore been found desirable to provide a disk storage system wherein the top cover is sealed to the lower base plate in a manner which reduces or eliminates warping or distortion of the head disk assembly caused by misregistered parts, which at the same time is conducive to automated assembly.
As aforementioned, in order to reduce the Z-height of the disk drive system, previous designs have focused on the means for attaching the spin motor to the lower base plate. In prior disk drive systems, the spin motor assembly is typically mechanically fastened to the lower base plate by various means, such as by screws, glue or press-fitting. For instance, in U.S. Pat. Nos. 4,814,913 and 5,025,336, the spin motor assembly is screwed to the lower base plate. It has been found, however, that mechanically fastening the spin motor to the lower base plate has led to disadvantages in the areas of contamination generation, sealing between parts, and the introduction of residual and transient stresses into the base plate. It has therefore been found desirable to provide a disk storage system which eliminates the necessity of joining a separate spin motor and base plate, and in turn, eliminates fasteners, gluing or press-fitting operations associated with joining separate components.